1. Field of the Invention
The present invention relates to an automatic travel controlling device and particularly to a device for guiding vehicles along lanes provided with lane lines, having a color such as white, and with side walls.
2. Description of the Prior Art
Heretofore, travel controlling systems have been developed with an object to reduce driving operations by the vehicle driver and to further improve safety.
For example, Japanese Patent Laid-Open Publication No. Hei 7-244717 discloses a technique for photographing lanes, such as with a CCD camera, and detecting lane lines from the obtained image, and based on the lane line positions detected in this manner, enables the control of the vehicle travel, particularly steering.
However, the difficulty of reliably detecting lane lines using the above-mentioned prior art was a problem because actual lanes have white lines which may be discontinuous or faint.
Even for lanes in which the white lines are not faint, there was a problem where the two lane lines could not be detected and the vehicle position also could not be detected, such as when the vehicle performs a course change, since the lane lines move outside the photographic range due to the camera's angle of view being fixed. Of course, in principle, the vehicle position can be determined as long as one of the two white lines defining a lane can be photographed. However, in practice, the vehicle position cannot be accurately detected due to fluctuations of the lane line positions within the image caused by pitching of the vehicle. (In comparison, if the two lane lines are detected, a center position between both lines becomes the center of the lane so that the vehicle position can be determined even under the influence of pitching.)